ALE #3 Energy
Name___________________________________
Energy general
1) Discuss how photosynthesis and respiration are related to each other, using the first
law of thermodynamics in your answer. The first law of thermodynamics states that
energy cannot be created or destroyed, only changed to different forms. In
photosynthesis, plants absorb energy from the sun, and store it in the chemical bonds of
glucose. This energy stored in glucose is then harvested by all organisms on earth (plants
and animals both) as fuel for cellular respiration. In cellular respiration, cells break down
glucose and store the energy from its bonds in the molecule ATP. ATP can then be used
to power all of the cell’s work. The products of photosynthesis, oxygen and glucose, are
the reactants of cellular respiration. The products of cellular respiration, carbon dioxide
and water, are the reactants of photosynthesis.
2) What is ATP and how is it generated? ATP is adenosine triphosphate. It is a highenergy carrier molecule, which is used to power all cellular work. ATP gives up
phosphate group to molecules, which gives them energy to react (called
phosphorylation). It is generated by electron transfer chains.
3) Why are enzymes important? How do enzymes work? Enzymes are important because
there is one unique type of enzyme to catalyze each chemical reaction. This means that
they speed up chemical reactions by lower the amount of activation energy required for
the reaction to proceed from reactants to products. Without enzymes, the reactions of
respiration would occur too slow to meet the ATP demands of a multicellular organism.
Enzymes help to lower the activation energy by helping substrates get together and
oriented them in a position favorable for the reaction to proceed. Enzymes are activated
by ATP, and they are not used up in the reaction. In other words, they are reusable.
Photosynthesis
4) What is the purpose of the Calvin cycle? What molecules are produced? The purpose
of the Calvin cycle is to convert carbon dioxide into glucose molecules. The molecule
produced in its reactions are glucose, ADP, and NADP+
5) Where do the oxygen atoms (in oxygen gas) come from in photosynthesis? Oxygen
gas is released as a byproduct of the splitting of water in the photosystem.
6) What is the immediate source of energy for the Calvin cycle? ATP and NADPH
7) Where do the light reactions of photosynthesis occur? (specific) The thylakoid
membrane of the chloroplast
8) Which pigment is directly involved in the light reactions of photosynthesis? What role
does it play in the light reactions? Chlorophyll is the main photosynthesis pigment.
Chlorophyll molecules work together to absorb photons of light. As the molecules
absorb sunlight, they kick their electrons up to a high energy state. These electrons are
then passed down the electron transfer chain, generating ATP.
9) In the following space, describe the steps of the light reactions. With the description
of each step, draw a diagram that helps to understand what happens in that step.
Description of step
Photosystem absorbs light, splitting water
into H+, electrons, and O2.
Further light absorption by the photosystem
kicks the electrons up to an excited state.
Excited electrons are passed along an
electron transport chain (proteins in the
thylakoid membrane)
Energy released at every step of electron
transport used to drive ATP synthesis
Drawing
Diagrams will vary. Use figures 7.10-7.12
as your guide.
Further light absorption by a second
photosystem kicks the electrons up to
another excited state, passing the electrons
off to generate NADPH.
10) Where do the Calvin cycle reactions occur? (specific) In the stroma of the
chloroplast.
11) Why is NADP+ important in photosynthesis? It is the final electron acceptor in the
electron transfer chain of the light reactions. It carries its high-energy electrons to the
Calvin cycle. Thus is a source of energy to power the Calvin cycle.
12) Why is chlorophyll green? It reflects green light and absorbs all other wavelengths of
visible light.
13) What is a photosystem and what do they do? Photosystems are units of chlorophyll
& accessory pigments. They work together to absorb a photon of light. The absorbtion of
light kicks electrons up to an excited, high energy state.
14) What products of the light reaction are REQUIRED by the Calvin cycle? ATP and
NADPH
Cellular Respiration
15) What is cellular respiration? Define. The breakdown of glucose to create ATP, which
is used to power all cellular work.
16) Fill in the following summary table for Aerobic cellular respiration:
Step:
Reactants (going into)
Products (coming out)
Glycolysis
Glucose, ATP
2 pyruvic acid, ATP,
NADH
Kreb’s cycle
Acetyl Co-A (derived
from pyruvic acid),
NAD+, FAD, ADP
NADH, FADH2, ADP,
O2
CO2, ATP, NADH,
FADH2
2
ATP, H20, NAD+, FAD
32-34
Electron transfer
chain
# ATP
produced
2
17) How is cellular respiration related to breathing? When we breathe in, oxygen enters
our lungs. Our arteries carry the oxygenated blood from our lungs to all of the cells of
our body. Our cells use the oxygen for the process of cellular respiration. Carbon
dioxide is released as a byproduct of the Krebs cycle. The CO2 is carried by our veins
back to the lungs, where we breathe it out.
18) Why is oxygen needed for Aerobic cellular respiration?
Oxygen is the final electron acceptor of the electron transfer chain.
19) If oxygen is not available to cells, how do they get energy from glucose? Glycolysis
can occur without oxygen, so cells can obtain a little bit of ATP (net 2 molecules of ATP)
even without oxygen.
20) Fill in the following summary table for Anaerobic cellular respiration:
Step:
Reactants (going into)
Products (coming out)
# ATP
produced (net)
2
1. Glycolysis
Glucose, ATP
2 pyruvic acid, ATP,
NADH
2. Lactic acid
fermentation - or
Pyruvic acid
Lactic acid
0
2. Alcoholic
fermentation
Pyruvic acid
alcohol
0